Western nations and Russia have traded accusations at the UN over the latest surge in violence in eastern Ukraine.
At the same, a senior member of an international monitoring team has blamed both sides in the conflict for breaking a ceasefire.
The diplomatic clash on Friday between European, US and Russian diplomats came a day after Ukraine warned of a possible "full-scale invasion" by Russia, following the worst fighting with pro-Russian separatists in months.
Alexander Hug, deputy head of the monitoring mission of the Organisation for Security and Cooperation in Europe's (OSCE), said both sides of the conflict were putting civilians at risk as the security situation deteriorates.
"Civilians continue to bear an unacceptable price in this conflict," Hug told an emergency meeting of the 15-nation Security Council.
"They are killed and wounded, as both sides continue to place military positions in and around civilian infrastructure. Their property and livelihoods have been destroyed."
Blame on Russia
The UK placed the blame for the new violence squarely on Russia.
"This was a separatist assault on Ukrainian military units," Matthew Rycroft, Britain's ambassador, said, adding that it was "clearly premeditated".
"The separatist forces are Russia's creation, they are Russia's tool. Russia has the capacity and the influence to control the separatist forces. It must exercise that influence."
Vitaly Churkin, Russian ambassador, presented the opposite view, blaming the latest fighting on Ukraine.
"If we allow Kiev to continue ... the situation could fall out of control," he said.
Samantha Power, US ambassador, cited Twitter announcements by separatist fighters boasting of a successful attack on Maryinka.
She said Russia continues to deny the "open secret" that it arms the rebels and sends Russian soldiers to die anonymously in neighbouring Ukraine, Reuters news agency reported.
The ambassadors of Lithuania and Ukraine said Ukraine had a right to defend itself against the Russian-backed rebels.
Ukraine and its NATO allies accuse Russia of sending weapons and troops to fight on behalf of separatists who control part of two provinces in its east.
Russia, which seized and annexed Ukraine's Crimea peninsula last year, denies its troops are participating.